Opacity occurs when light undergoes internal scattering in the material, leading to directional changes, and subsequently returns to the eye of the viewer from a different direction. Such changes in directions are due to light rays entering regions having different refractive indexes (“RIs”) in the material. In general, the more scattering and directional changes, the higher the opacity of the material may be. Thus, if the light rays penetrate through a film in air, the film may appear transparent if the light rays travel through the film with few directional changes in the film. On the other hand, the film may appear translucent if some of the light rays are scattered; and opaque if all of the light rays are scattered and/or reflected, resulting in no light rays travelling through the film.
Pre-existing approaches to increase opacity of a formulation product include increasing the content of the formulation constituent having a high RI. Titanium dioxide (TiO2), or titania, has a relatively high RI (about 2.5). Titanium dioxide pigments are frequently used in many industries, such as ink, paint, cosmetics, and personal care, to impart opacity in formulated products.